class Mongo::Cursor
Client-side representation of an iterator over a query result set on the server.
A Cursor
is not created directly by a user. Rather, CollectionView
creates a Cursor
in an Enumerable module method.
@example Get an array of 5 users named Emily.
users.find({:name => 'Emily'}).limit(5).to_a
@example Call a block on each user doc.
users.find.each { |doc| puts doc }
@note The Cursor
API is semipublic. @api semipublic
Attributes
The resume token tracked by the cursor for change stream resuming
@return [ BSON::Document | nil ] The cursor resume token. @api private
@api private
@return [ Collection::View
] view The collection view.
Public Class Methods
Finalize the cursor for garbage collection. Schedules this cursor to be included in a killCursors operation executed by the Cluster's CursorReaper.
@example Finalize the cursor.
Cursor.finalize(id, cluster, op, server)
@param [ Integer ] cursor_id The cursor's id. @param [ Mongo::Cluster
] cluster The cluster associated with this cursor and its server. @param [ Hash ] op_spec The killCursors operation specification. @param [ Mongo::Server
] server The server to send the killCursors operation to.
@return [ Proc ] The Finalizer.
@since 2.3.0
# File lib/mongo/cursor.rb, line 104 def self.finalize(cursor_id, cluster, op_spec, server, session) proc do cluster.schedule_kill_cursor(cursor_id, op_spec, server) session.end_session if session && session.implicit? end end
Creates a Cursor
object.
@example Instantiate the cursor.
Mongo::Cursor.new(view, response, server)
@param [ CollectionView ] view The CollectionView
defining the query. @param [ Operation::Result
] result The result of the first execution. @param [ Server
] server The server this cursor is locked to. @param [ Hash ] options The cursor options.
@option options [ true, false ] :disable_retry Whether to disable
retrying on error when sending getMore operations (deprecated, getMore operations are no longer retried)
@option options [ true, false ] :retry_reads Retry reads (following
the modern mechanism), default is true
@since 2.0.0
# File lib/mongo/cursor.rb, line 68 def initialize(view, result, server, options = {}) @view = view @server = server @initial_result = result @remaining = limit if limited? @cursor_id = result.cursor_id @coll_name = nil @options = options @session = @options[:session] register if @cursor_id && @cursor_id > 0 ObjectSpace.define_finalizer(self, self.class.finalize(@cursor_id, cluster, kill_cursors_op_spec, server, @session)) end end
Public Instance Methods
Get the batch size.
@example Get the batch size.
cursor.batch_size
@return [ Integer ] The batch size.
@since 2.2.0
# File lib/mongo/cursor.rb, line 223 def batch_size @view.batch_size && @view.batch_size > 0 ? @view.batch_size : limit end
Is the cursor closed?
@example Is the cursor closed?
cursor.closed?
@return [ true, false ] If the cursor is closed.
@since 2.2.0
# File lib/mongo/cursor.rb, line 235 def closed? !more? end
Get the parsed collection name.
@example Get the parsed collection name.
cursor.coll_name
@return [ String ] The collection name.
@since 2.2.0
# File lib/mongo/cursor.rb, line 247 def collection_name @coll_name || collection.name end
Iterate through documents returned from the query.
@example Iterate over the documents in the cursor.
cursor.each do |doc| ... end
@return [ Enumerator ] The enumerator.
@since 2.0.0
# File lib/mongo/cursor.rb, line 133 def each # If we already iterated past the first batch (i.e., called get_more # at least once), the cursor on the server side has advanced past # the first batch and restarting iteration from the beginning by # returning initial result would miss documents in the second batch # and subsequent batches up to wherever the cursor is. Detect this # condition and abort the iteration. # # In a future driver version, each would either continue from the # end of previous iteration or would always restart from the # beginning. if @get_more_called raise NotImplementedError, 'Cannot restart iteration of a cursor which issued a getMore' end # To maintain compatibility with pre-2.10 driver versions, reset # the documents array each time a new iteration is started. @documents = nil loop do document = try_next yield document if document end rescue StopIteration => e return self end
Execute a getMore command and return the batch of documents obtained from the server.
@return [ Array<BSON::Document> ] The batch of documents
@api private
# File lib/mongo/cursor.rb, line 284 def get_more @get_more_called = true # Modern retryable reads specification prohibits retrying getMores. # Legacy retryable read logic used to retry getMores, but since # doing so may result in silent data loss, the driver no longer retries # getMore operations in any circumstance. # https://github.com/mongodb/specifications/blob/master/source/retryable-reads/retryable-reads.rst#qa process(get_more_operation.execute(@server)) end
Get the cursor id.
@example Get the cursor id.
cursor.id
@note A cursor id of 0 means the cursor was closed on the server.
@return [ Integer ] The cursor id.
@since 2.2.0
# File lib/mongo/cursor.rb, line 261 def id @cursor_id end
Get a human-readable string representation of Cursor
.
@example Inspect the cursor.
cursor.inspect
@return [ String ] A string representation of a Cursor
instance.
@since 2.0.0
# File lib/mongo/cursor.rb, line 119 def inspect "#<Mongo::Cursor:0x#{object_id} @view=#{@view.inspect}>" end
Get the number of documents to return. Used on 3.0 and lower server versions.
@example Get the number to return.
cursor.to_return
@return [ Integer ] The number of documents to return.
@since 2.2.0
# File lib/mongo/cursor.rb, line 274 def to_return use_limit? ? @remaining : (batch_size || 0) end
Return one document from the query, if one is available.
This method will wait up to max_await_time_ms milliseconds for changes from the server, and if no changes are received it will return nil. If there are no more documents to return from the server, or if we have exhausted the cursor, it will raise a StopIteration exception.
@note This method is experimental and subject to change.
@return [ BSON::Document | nil ] A document. @api private
# File lib/mongo/cursor.rb, line 172 def try_next if @documents.nil? # Since published versions of Mongoid have a copy of old driver cursor # code, our dup call in #process isn't invoked when Mongoid query # cache is active. Work around that by also calling dup here on # the result of #process which might come out of Mongoid's code. @documents = process(@initial_result).dup # the documents here can be an empty array, hence # we may end up issuing a getMore in the first try_next call end if @documents.empty? # On empty batches, we cache the batch resume token cache_batch_resume_token if more? if exhausted? kill_cursors raise StopIteration end @documents = get_more else raise StopIteration end else # cursor is closed here # keep documents as an empty array end # If there is at least one document, cache its _id if @documents[0] cache_resume_token(@documents[0]) end # Cache the batch resume token if we are iterating # over the last document, or if the batch is empty if @documents.size <= 1 cache_batch_resume_token end return @documents.shift end
Private Instance Methods
# File lib/mongo/cursor.rb, line 307 def cache_batch_resume_token @resume_token = @post_batch_resume_token if @post_batch_resume_token end
# File lib/mongo/cursor.rb, line 301 def cache_resume_token(doc) if doc[:_id] && doc[:_id].is_a?(Hash) @resume_token = doc[:_id] && doc[:_id].dup.freeze end end
# File lib/mongo/cursor.rb, line 330 def end_session @session.end_session if @session && @session.implicit? end
# File lib/mongo/cursor.rb, line 297 def exhausted? limited? ? @remaining <= 0 : false end
# File lib/mongo/cursor.rb, line 311 def get_more_operation if @server.features.find_command_enabled? spec = Builder::GetMoreCommand.new(self, @session).specification else spec = Builder::OpGetMore.new(self).specification end Operation::GetMore.new(spec) end
# File lib/mongo/cursor.rb, line 320 def kill_cursors unregister read_with_one_retry do kill_cursors_operation.execute(@server) end ensure end_session @cursor_id = 0 end
# File lib/mongo/cursor.rb, line 338 def kill_cursors_op_spec if @server.features.find_command_enabled? Builder::KillCursorsCommand.new(self).specification else Builder::OpKillCursors.new(self).specification end end
# File lib/mongo/cursor.rb, line 334 def kill_cursors_operation Operation::KillCursors.new(kill_cursors_op_spec) end
# File lib/mongo/cursor.rb, line 376 def limit @view.send(:limit) end
# File lib/mongo/cursor.rb, line 346 def limited? limit ? limit > 0 : false end
# File lib/mongo/cursor.rb, line 350 def more? @cursor_id != 0 end
# File lib/mongo/cursor.rb, line 354 def process(result) @remaining -= result.returned_count if limited? @coll_name ||= result.namespace.sub("#{database.name}.", '') if result.namespace unregister if result.cursor_id == 0 @cursor_id = result.cursor_id if result.respond_to?(:post_batch_resume_token) @post_batch_resume_token = result.post_batch_resume_token end end_session if !more? # Since our iteration code mutates the documents array by calling #shift # on it, duplicate the documents here to permit restarting iteration # from the beginning of the cursor as long as get_more was not called result.documents.dup end
# File lib/mongo/cursor.rb, line 380 def register cluster.register_cursor(@cursor_id) end
# File lib/mongo/cursor.rb, line 384 def unregister cluster.unregister_cursor(@cursor_id) end
# File lib/mongo/cursor.rb, line 372 def use_limit? limited? && batch_size >= @remaining end